Modified conjugated diene-based polymer and rubber composition containing same

ABSTRACT

The present invention provides a modified conjugated diene polymer in which a phenoxy group of a polar group-containing phenoxy compound is bonded to at least one selected from the group consisting of the end, main chain, and side chain of a conjugated diene polymer, which can further improve a rubber composition in the low-heat-generation property and abrasion resistance, and a rubber composition using the same.

TECHNICAL FIELD

The present invention relates to a modified conjugated diene polymerwhich can improve the low-heat-generation property and abrasionresistance, and a rubber composition containing the same.

BACKGROUND ART

In recent years, from the viewpoint of conserving energy, tires having asmall rolling resistance are demanded. For this reason, as a rubbercomposition used in a tire tread and the like, a rubber compositionhaving a low tan δ and excellent low-heat-generation property isdemanded. Further, the rubber composition for use in a tread is requiredto have excellent abrasion resistance as well as excellentlow-heat-generation property. For meeting such demands, in order toimprove the low-heat-generation property and abrasion resistance of therubber composition, various attempts are made to improve the affinity ofa filler, such as carbon black or silica, with a rubber component in therubber composition.

For example, PTL 1 has proposed a modified natural rubber which isobtained by adding a polar group-containing compound to at least onenatural rubber raw material selected from the group consisting ofnatural rubber, a natural rubber latex coagulation product, and anatural rubber cup lump, and applying a mechanical shear force to theresultant mixture to cause graft polymerization or addition.

PTL 2 discloses a modified natural rubber latex which is obtained byadding a polar group-containing mercapto compound to a natural rubberlatex so that the polar group-containing mercapto compound is added tonatural rubber molecules in the natural rubber latex.

Further, PTLs 3 to 6 have proposed a modified natural rubber which isobtained by graft-polymerizing various polar group-containing monomerson a natural rubber latex.

However, for obtaining a rubber component which has a further improvedaffinity with a reinforcing filler formed from carbon black and/orsilica so as to enable the rubber composition to be further improved inlow-heat-generation property and abrasion resistance, the modifiedconjugated diene polymer is needed to be further improved.

CITATION LIST Patent Literature

-   PTL 1: JP-A 2006-152171-   PTL 2: JP-A 2006-152045-   PTL 3: JP-A 2004-359716-   PTL 4: JP-A 2004-359717-   PTL 5: JP-A 2004-359713-   PTL 6: JP-A 2004-359714

SUMMARY OF INVENTION Technical Problem

In this situation, an object of the present invention is to provide amodified conjugated diene polymer which can further improve a rubbercomposition in the low-heat-generation property and abrasion resistance,and a rubber composition using the same.

Solution to Problem

The present inventor made attempts to modify a conjugated diene polymerwith various compounds in order to achieve the above object, and hasfound that the object of the present invention can be achieved bymodifying a conjugated diene polymer with a specific compound, and thepresent invention has been completed.

Specifically, the present invention is directed to a modified conjugateddiene polymer in which a phenoxy group of a polar group-containingphenoxy compound is bonded to at least one selected from the groupconsisting of the end, main chain, and side chain of a conjugated dienepolymer.

Advantageous Effects of Invention

In the present invention, there can be provided a modified conjugateddiene polymer which can further improve a rubber composition in thelow-heat-generation property and abrasion resistance, and a rubbercomposition using the same.

DESCRIPTION OF EMBODIMENTS [Modified Conjugated Diene Polymer]

The present invention provides a modified conjugated diene polymer inwhich a phenoxy group of a polar group-containing phenoxy compound isbonded to at least one selected from the group consisting of the end,main chain, and side chain of a conjugated diene polymer.

The conjugated diene polymer used in the modified conjugated dienepolymer of the present invention means a polymer which does not containa non-conjugated olefin as a monomer unit component (a part of acopolymer). Styrene is not included in the non-conjugated olefin.

With respect to the conjugated diene polymer, there is no particularlimitation, and the conjugated diene polymer may be any of a dienehomopolymer and a diene copolymer, and can be appropriately selectedaccording to the purpose, and, for example, there can be mentionednatural rubber (NR), various polybutadiene rubbers (BR), a syntheticpolyisoprene rubber (IR), various styrene-butadiene copolymer rubbers(SBR), a styrene-isoprene copolymer rubber (SIR), astyrene-isoprene-butadiene terpolymer rubber, an isoprene-butadienecopolymer rubber (IBR), an acrylonitrile-butadiene copolymer rubber(NBR), and a chloroprene rubber. Of these, at least one selected fromnatural rubber and an emulsion-polymerized styrene-butadiene copolymerrubber is preferred, and natural rubber is especially preferred.

[Polar Group-Containing Phenoxy Compound]

The polar group-containing phenoxy compound in the present invention ispreferably a polar group-containing phenolic compound represented by thefollowing general formula (I).

In the general formula (I), R is a single bond or a hydrocarbon grouphaving 1 to 10 carbon atoms, and X is a polar group. n is 1 to 5. When aplurality of —R—X are present, they may be the same or different.Further, a plurality of X's may be bonded to a single R, and, in thiscase, X's may be the same or different.

In the present invention, the wording “R is a single bond” means that Xadjacent to R in the general formula (I) is bonded directly to anaromatic ring through a single bond.

It is preferred that the polar group of the polar group-containingphenoxy compound in the present invention is at least one selected fromthe group consisting of an amino group, an imino group, a nitrile group,an ammonium group, an imide group, an amide group, a hydrazo group, anazo group, a diazo group, a sulfide group, a disulfide group, a sulfonylgroup, a sulfinyl group, a thiocarbonyl group, a hydroxyl group, acarboxyl group, a carbonyl group, an epoxy group, an oxycarbonyl group,a nitrogen-containing heterocyclic group, an oxygen-containingheterocyclic group, a tin-containing group, and an alkoxysilyl group. Ofthese, the polar group is especially preferably at least one selectedfrom an amino group and a carboxyl group. In this case, at least oneselected from an amino group and a carboxyl group may be directly bondedto an aromatic ring, or at least one selected from an amino group and acarboxyl group may be bonded to a hydrocarbon group directly bonded toan aromatic ring. Alternatively, at least one selected from an aminogroup and a carboxyl group may be directly bonded to an aromatic ring,and another one may be bonded to a hydrocarbon group directly bonded tothe aromatic ring. At least one selected from an amino group and acarboxyl group may be present in at least one selected from the groupconsisting of a peptide-derived monovalent group and a protein-derivedmonovalent group.

It is preferred that the modified conjugated diene polymer of thepresent invention has both an amino group and a carboxyl group as thepolar group.

The polar group-containing phenoxy compound in the present invention ispreferably at least one polar group-containing (thio)phenolic compoundselected from the group consisting of tyrosine, amidol, 4-aminophenol,4-(aminomethyl)phenol, 4-hydroxybenzoic acid, 4-hydroxybenzyl alcohol,4-triethoxysilylphenol, 4-[(2-triethoxysilyl)ethyl]phenol, and4-[(2-triethoxysilyl)ethylthio]phenol, and at least one selected fromthe group consisting of a peptide having tyrosine and a protein havingtyrosine. Of these, the polar group-containing phenoxy compound isfurther preferably at least one selected from the group consisting oftyrosine, a peptide having tyrosine, and a protein having tyrosine.

The modified conjugated diene polymer of the present invention ispreferably formed in a way such that the phenoxy group of the polargroup-containing phenoxy compound produces phenoxy radials due to aphenol oxidase, such as laccase, and the resultant radials are added toat least one site of the conjugated diene polymer selected from the endof the conjugated diene polymer, a double bond of the main chain, adouble bond of the side chain, the α-position of a double bond of themain chain, and the α-position of a double bond of the side chain toform a modified conjugated diene polymer.

As a phenol oxidase, laccase is preferred. Laccase is an oxidase havingthe ability to oxidize a phenol.

As examples of a reaction in which the conjugated diene polymer isreacted with the polar group-containing phenoxy compound to form themodified conjugated diene polymer of the present invention, the reactionformula (II) and reaction formula (III) are shown below. The reactionformula (II) shows a case in which a reaction occurs at the main chainof the conjugated diene polymer. The modified conjugated diene polymer(II-a) shows a case in which the polar group-containing phenoxy compoundhas been added to a double bond of the main chain of the conjugateddiene polymer, and the modified conjugated diene polymer (II-b) shows acase in which the polar group-containing phenoxy compound has been addedto the α-position of a double bond of the main chain of the conjugateddiene polymer.

The reaction formula (III) shows a case in which a reaction occurs atthe side chain or the α-position of a double bond of the side chain ofthe conjugated diene polymer. The modified conjugated diene polymers(III-a) and (III-b) show a case in which the polar group-containingphenoxy compound has been added to a double bond of the side chain ofthe conjugated diene polymer, and the modified conjugated diene polymer(III-c) shows a case in which the polar group-containing phenoxycompound has been added to the α-position of a double bond of the sidechain of the conjugated diene polymer.

The reaction for forming the modified conjugated diene polymer of thepresent invention is not limited to the reaction formula (II) andreaction formula (III).

In the present invention, the modification degree (millimole) means anamount [mmol (millimole)] of the polar group-containing phenoxy compoundbonded in 100 g of the modified conjugated diene polymer. In the presentinvention, the amount of the polar group-containing phenoxy compoundbonded in 100 g of the modified conjugated diene polymer is preferably0.005 to 55 mmol, more preferably 0.01 to 27 mmol, further preferably0.05 to 16 mmol.

Further, the addition amount means an amount (part(s) by mass) of thepolar group-containing phenoxy compound bonded to 100 parts by mass ofthe modified conjugated diene polymer.

The modification degree in the present invention (the amount [mmol(millimole)] of the polar group-containing phenoxy compound bonded in100 g of the modified conjugated diene polymer) is quantitativelydetermined by means of a pyrolysis gas chromatography mass spectrometer(GC-MS). When the polar group-containing phenoxy compound contains apeptide-derived monovalent group, a protein-derived monovalent group, oran amino acid-derived monovalent group (for example, the polargroup-containing phenoxy compound containing an amino acid-derivedmonovalent group includes tyrosine), the modification degree isdetermined as follows. A sample to be tested is immersed in 6 Nhydrochloric acid at 110° C. for 24 hours to cause the contained proteinor peptide to suffer a hydrolysis reaction, and the noncovalent-bondedamino acid is removed by reprecipitation. As a result, only the aminoacid covalent-bonded to the polymer remains, and it is quantitativelydetermined by a pyrolysis GC-MS. The amount of the amino acidcovalent-bonded to the modified conjugated diene polymer is taken as anamount of the polar group-containing phenoxy compound bonded.

The modified conjugated diene polymer of the present invention isproduced, for example, as follows.

In the present invention, generally, the above-mentioned polargroup-containing phenoxy compound is added to a solution obtained byadding water and optionally an emulsifying agent to a latex, an aqueousemulsion, or an aqueous dispersion of at least one conjugated dienepolymer selected from natural rubber and a synthetic conjugated dienepolymer, and stirred at a predetermined temperature to cause the polargroup-containing phenoxy compound to undergo an addition reaction to adouble bond of or the α-position of a double bond of at least one of themain chain and side chain of the conjugated diene polymer molecule inthe latex, aqueous emulsion, or aqueous dispersion of the conjugateddiene polymer. As a result, the phenoxy group of the polargroup-containing phenoxy compound is bonded, particularly, covalentlybonded to at least one selected from the group consisting of the end,main chain, and side chain of the conjugated diene polymer to obtain amodified conjugated diene polymer. In the addition of the polargroup-containing phenoxy compound to the latex, aqueous emulsion, oraqueous dispersion of the conjugated diene polymer, a phenol oxidase(preferably laccase) and, if desired, an emulsifying agent may be addedin advance to the latex, aqueous emulsion, or aqueous dispersion of theconjugated diene polymer, or the polar group-containing phenoxy compoundmay be emulsified using an emulsifying agent and then added, togetherwith a phenol oxidase (preferably laccase), to the latex, aqueousemulsion, or aqueous dispersion of the conjugated diene polymer. Ifnecessary, an organic peroxide may be further added. With respect to theemulsifying agent which can be used in emulsifying the latex, aqueousemulsion, or aqueous dispersion of the conjugated diene polymer and/orthe polar group-containing phenoxy compound, there is no particularlimitation, and examples of emulsifying agents include nonionicsurfactants, such as polyoxyethylene lauryl ether.

For mixing a filler, such as carbon black or silica, into the modifiedconjugated diene polymer of the present invention to improve thelow-heat-generation property and abrasion resistance of a rubbercomposition without causing the processability of the rubber compositionto be poor, it is important that the polar group-containing phenoxycompound is introduced in a small amount uniformly into the individualconjugated diene polymer molecules. Therefore, the above-mentionedmodification reaction is preferably conducted while stirring, forexample, the ingredients including the latex, aqueous emulsion, oraqueous dispersion of the conjugated diene polymer, and the polargroup-containing phenoxy compound and others are charged into a reactionvessel, and subjected to reaction at 30 to 80° C. for 10 minutes to 24hours to obtain a latex, aqueous emulsion, or aqueous dispersion of amodified conjugated diene polymer having the polar group-containingphenoxy compound added to conjugated diene polymer molecules. Thethus-obtained latex, aqueous emulsion, or aqueous dispersion of themodified conjugated diene polymer may be used as such in the form of alatex, aqueous emulsion, or aqueous dispersion, or may be furthercoagulated and dried and used in a solid state. When used in a rubbercomposition, the modified conjugated diene polymer is preferably used inthe form of a solid rubber. When used in the form of a solid rubber, thelatex, aqueous emulsion, or aqueous dispersion of the modifiedconjugated diene polymer is coagulated, and washed and then dried usinga dryer, such as a vacuum dryer, an air dryer, a drum dryer, or adouble-screw extruder, obtaining a modified conjugated diene polymer ina solid state. With respect to the coagulant used for coagulating thelatex, aqueous emulsion, or aqueous dispersion of the modifiedconjugated diene polymer, there is no particular limitation, butexamples of coagulants include acids, such as formic acid and sulfuricacid, and salts, such as sodium chloride.

When the modified conjugated diene polymer of the present invention is amodified natural rubber, a protein containing tyrosine contained in anatural rubber latex also participates in the reaction, and therefore,even when the amount of the polar group-containing phenoxy compoundadded is 0 part by mass, a modified natural rubber may be formed.Therefore, the amount of the polar group-containing phenoxy compoundadded to the conjugated diene polymer before being modified is, relativeto 100 parts by mass of the conjugated diene polymer, preferably 0 to 10parts by mass, more preferably 0 to 7 parts by mass, further preferably0 to 5 parts by mass, especially preferably 0 to 3 parts by mass. Whenthe amount of the polar group-containing phenoxy compound added is 3parts by mass or less, inherent physical properties of the conjugateddiene polymer, such as viscoelasticity and S—S characteristics(stress-strain curve measured by a tensile tester), are not largelychanged, and not only can inherent excellent physical properties of theconjugated diene polymer be secured, but also the processability of therubber composition can be especially advantageously maintained orimproved.

Further, in the modified synthetic conjugated diene polymer other thannatural rubber, the amount of the polar group-containing phenoxycompound added to the synthetic conjugated diene polymer is, relative to100 parts by mass of the synthetic conjugated diene polymer, preferably0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass,further preferably 0.1 to 3 parts by mass. When the amount of the polargroup-containing phenoxy compound added is 0.1 part by mass or more, itis possible to especially advantageously improve the rubber compositionin the low-heat-generation property and abrasion resistance. Further,when the amount of the polar group-containing phenoxy compound added is3 parts by mass or less, inherent physical properties of the conjugateddiene polymer are not largely changed, and not only can inherentexcellent physical properties of the conjugated diene polymer besecured, but also the processability of the rubber composition can beespecially advantageously maintained or improved.

The rubber component of the rubber composition of the present inventioncan contain, in addition to the modified conjugated diene polymer,another diene rubber in such an amount that the object of the presentinvention can be achieved. For example, it is preferred that, in therubber component, the modified conjugated diene polymer is contained inan amount of 50 to 100% by mass and another diene rubber is contained inan amount of 50 to 0% by mass. As another diene rubber, at least oneselected from the group consisting of natural rubber, astyrene-butadiene copolymer rubber, a polybutadiene rubber, apolyisoprene rubber, an acrylonitrile-butadiene copolymer rubber, abutyl rubber, a halogenated butyl rubber (such as Cl-IIR or Br-IIR), anethylene-propylene-diene terpolymer rubber (EPDM), an ethylene-butadienecopolymer rubber (EBR), a propylene-butadiene copolymer rubber (PBR),and a chloroprene rubber, or the like can be used. One type of themodified conjugated diene polymer may be individually used, or two ormore types of the modified conjugated diene polymers may be used in theform of a blend, and one type of the other diene rubber may beindividually used, or two or more types of the other diene rubbers maybe used in the form of a blend.

It is preferred that the rubber composition of the present inventionfurther contains a filler, in addition to a rubber component containingthe modified conjugated diene polymer. With respect to the amount of thefiller mixed, there is no particular limitation, but the amount of thefiller is, relative to 100 parts by mass of the rubber componentcontaining the modified conjugated diene polymer, preferably in therange of from 5 to 150 parts by mass, further preferably in the range offrom 10 to 100 parts by mass. When the amount of the filler mixed is 5parts by mass or more, reinforcing properties can be advantageouslyobtained, and, when the amount of the filler mixed is 150 parts by massor less, it is possible to prevent the processability from becomingpoor.

As a filler mixed into the rubber composition of the present invention,at least one selected from carbon black and an inorganic filler is used.

With respect to the carbon black, there is no particular limitation,and, for example, at least one carbon black selected from the groupconsisting of SAF, ISAF, IISAF, N339, HAF, FEF, GPF, and SRF grades of ahigh, medium, or low structure is preferably used, especially, at leastone carbon black selected from the group consisting of SAF, ISAF, IISAF,N339, HAF, and FEF grades is preferably used. The nitrogen adsorptionspecific surface area (N₂SA, as measured in accordance with JIS K6217-2:2001) of carbon black is preferably 30 to 250 m²/g.

One type of the carbon black may be individually used, or two or moretypes of the carbon black may be used in combination. In the presentinvention, carbon black is not included in the inorganic filler.

With respect to the inorganic filler mixed into the rubber compositionof the present invention, from the viewpoint of achieving both thelow-heat-generation property and the abrasion resistance, silica ispreferred. As silica, any commercially available products can be used,and, of these, wet precipitated (precipitated) silica, wet gelledsilica, dry silica, or colloidal silica is preferably used, and wetprecipitated silica is especially preferably used. Silica preferably hasa BET specific surface area (as measured in accordance with ISO 5794/1)of 40 to 350 m²/g. The silica having a BET surface area in this rangehas an advantage in that both the rubber reinforcing properties anddispersibility in the rubber component can be achieved. From this pointof view, silica having a BET surface area in the range of from 80 to 350m²/g is further preferred, and silica having a BET surface area in therange of from 120 to 350 m²/g is especially preferred. As theabove-mentioned silica, commercially available products, such as tradename “Nipsil AQ” (BET specific surface area=205 m²/g), “Nipsil KQ”,manufactured by Tosoh Silica Corporation, and trade name “Ultrasil VN3”(BET specific surface area=175 m²/g), manufactured by Degussa AG, can beused.

With respect to the inorganic filler mixed into the rubber compositionof the present invention, an inorganic compound represented by thefollowing general formula (IV) can be used instead of silica or inaddition to silica.

dM¹ ·xSiO_(y) ·zH₂O  (IV)

In the general formula (IV) above, M¹ is at least one selected from ametal selected from the group consisting of aluminum, magnesium,titanium, calcium, and zirconium, an oxide and a hydroxide of the metal,a hydrate thereof, and a carbonate of the metal, and d, x, y, and z are,respectively, an integer of 1 to 5, an integer of 0 to 10, an integer of2 to 5, and an integer of 0 to 10.

When both x and z in the general formula (IV) are 0, the inorganiccompound is at least one metal selected from aluminum, magnesium,titanium, calcium, and zirconium, an oxide of the metal, or a hydroxideof the metal.

In the general formula (IV) above, M¹ is preferably at least oneselected from aluminum metal, an oxide and a hydroxide of aluminum, ahydrate thereof, and a carbonate of aluminum, and is especiallypreferably aluminum hydroxide [Al(OH)₃].

With respect to the inorganic filler in the present invention, silicamay be solely used, or silica and one type or more of the inorganiccompound represented by the general formula (IV) may be used incombination.

In the rubber composition of the present invention, various mixingadditives generally mixed into a rubber composition, e.g., avulcanization activator, such as stearic acid, resin acid, or zincoxide, a vulcanization accelerator, an antioxidant, and a softeningagent are kneaded, if necessary, in the first stage or the final stagefor kneading, or in an intermediate stage between the first stage andthe final stage.

In the present invention, as a kneading apparatus, a Banbury mixer, anintermeshing internal mixer, a roll, an intensive mixer, a kneader, adouble-screw extruder, or the like is used.

EXAMPLES

Hereinbelow, the present invention will be described in more detail withreference to the following Examples, which should not be construed aslimiting the scope of the present invention.

The addition amount, modification degree, low-heat-generation property(tan δ index), and abrasion resistance (index) were evaluated by themethods described below.

1. Addition Amount

The addition amount is an amount [parts by weight] of the polargroup-containing phenoxy compound bonded to 100 parts by weight of themodified conjugated diene polymer, and was quantitatively determined bymeans of a pyrolysis gas chromatography mass spectrometer (GC-MS).

2. Modification Degree

The modification degree is an amount [mmol (millimole)] of the polargroup-containing phenoxy compound bonded in 100 g of the modifiedconjugated diene polymer, and was quantitatively determined by means ofa pyrolysis gas chromatography mass spectrometer (GC-MS). When the polargroup-containing phenoxy compound contains a peptide-derived monovalentgroup, a protein-derived monovalent group, and an amino acid-derivedmonovalent group, the modification degree is determined as follows. Asample to be tested is immersed in 6 N hydrochloric acid at 110° C. for24 hours to cause the contained protein or peptide to suffer ahydrolysis reaction, and the noncovalent-bonded amino acid is removed byreprecipitation. As a result, only the amino acid covalent-bonded to thepolymer remains, and it is quantitatively determined by a pyrolysisGC-MS, and the amount of the amino acid covalent-bonded to the modifiedconjugated diene polymer was taken as an amount of the polargroup-containing phenoxy compound bonded.

3. Low-Heat-Generation Property (Tan δ Index)

Using a spectrometer (dynamic viscoelasticity measuring tester),manufactured by Ueshima Seisakusho Co., Ltd., (E″/E′)=tan δ was measuredunder conditions that the frequency was 52 Hz, the initial strain was10%, the measurement temperature was 60° C., and the dynamic strain was1%, and was determined as an index represented by the expression belowin which the tan δ of the vulcanized rubber composition 1 in ComparativeExample 1 is taken as 100. The smaller the index value, the moreexcellent the low-heat-generation property, or the smaller thehysteresis loss.

Low-heat-generation property index=[(tan δ of the vulcanized rubbercomposition tested)/(tan δ of the vulcanized rubber composition 1obtained in Comparative Example 1)]×100

4. Abrasion Resistance (Index)

In accordance with JIS K 6264-2:2005, using a Lambourn abrasion tester,a test was conducted at room temperature under conditions such that theslip ratio was 25%, and a reciprocal of an abrasion amount wasdetermined as an index represented by the expression below in which thevalue of the vulcanized rubber composition 1 or 2 in Comparative Example1 is taken as 100. The larger the index value, the more excellent theabrasion resistance.

Abrasion resistance index=[(Abrasion amount of the vulcanized rubbercomposition 1 or 2 in Comparative Example 1)/(Abrasion amount of thevulcanized rubber composition tested)]×100

Production Example 1 (Modification Reaction Step for a Natural RubberLatex)

Water was added to a field latex of natural rubber to obtain a latexhaving a dry rubber concentration of 30% by mass. 2,000 g of theobtained latex was charged into a stainless steel reaction vesselequipped with a stirrer and a temperature control jacket, and a mixture,which was preliminarily prepared by adding 10 mL of water and 90 mg ofan emulsifying agent [EMULGEN 1108, manufactured by Kao Corporation] to10.8 g of tyrosine (1.8 parts by mass, relative to 100 parts by mass ofthe natural rubber component) and 0.6 g of laccase (trade name“NS81268”, manufactured by Novozymes) and emulsifying the resultantmixture, was added to the latex, and subjected to reaction at 60° C. for8 hours while stirring to obtain a modified natural rubber latex.

(Coagulation and Drying Step)

Then, formic acid was added to the above-obtained modified naturalrubber latex to adjust the pH to 4.7, thereby coagulating the modifiednatural rubber latex. The thus-obtained solid material was subjected totreatment using a scraper five times, and passed through a shredder tobe in a crumb form and then, dried using a hot-air dryer at 110° C. for210 minutes to obtain a modified conjugated diene polymer A which is amodified natural rubber. An analysis was made to determine an additionamount of tyrosine in the obtained modified conjugated diene polymer A(amount of the tyrosine bonded to the natural rubber). As a result, theaddition amount of tyrosine was found to be 0.24 part by mass, relativeto 100 parts by mass of the rubber component in the natural rubber latexbefore being modified. The modification degree was 1.3 mmol (millimole).

Production Examples 2 to 8

Modified conjugated diene polymers B to H were individually obtained inthe same manner as in Production Example 1 above except that, instead of10.8 g of tyrosine (1.8 parts by mass), as a polar group-containingphenoxy compound, the polar group-containing phenoxy compounds shown inTable 1 were individually added in the respective amounts shown inTable 1. Further, an analysis was made in the same manner as in theanalysis for the modified conjugated diene polymer A to determine anaddition amount and modification degree of the modified conjugated dienepolymers B to H, and the results shown in Table 1 were obtained.

Production Example 9

Vinyltriethoxysilane and 4-hydroxybenzenethiol in an equimolar amountwere first placed in a Schlenk flask, and azobisisobutyronitrile (AIBN)in a 1/100 molar amount was further placed in the flask, and theresultant mixture was subjected to reaction at 170° C. for 10 hourswhile stirring, and the resultant product was subjected to vacuumdistillation (140 to 143° C., 0.1 torr or less), and a massspectrometric analysis made on the product confirmed that4-[(2-triethoxysilyl)ethylthio]phenol was formed. A modified conjugateddiene polymer I was obtained in the same manner as in Production Example1 above except that, instead of 10.8 g of tyrosine (1.8 parts by mass),as a polar group-containing phenoxy compound, the above-obtained4-[(2-triethoxysilyl)ethylthio]phenol was added in the amount shown inTable 1. Further, an analysis was made in the same manner as in theanalysis for the modified conjugated diene polymer A to determine anaddition amount and modification degree of the modified conjugated dienepolymer I, and the results shown in Table 1 were obtained.

Production Example 10

The above-mentioned natural rubber latex was not subjected tomodification reaction step but was directly coagulated and dried toprepare an unmodified conjugated diene polymer.

TABLE 1 Modifica- Type of polar group-containing Amount Addition amounttion degree Product phenoxy compound (parts by mass) (parts by mass)(mmol) Production Modified conjugated diene polymer A Tyrosine *1 1.80.24 1.3 Example 1 Production Modified conjugated diene polymer BPeptide having tyrosine at end *2 2.0 0.20 0.15 Example 2 ProductionModified conjugated diene polymer C Protein having tyrosine at end *32.0 0.16 0.06 Example 3 Production Modified conjugated diene polymer DAmidol *4 2.0 0.26 1.3 Example 4 Production Modified conjugated dienepolymer E 4-Aminophenol *5 1.1 0.14 1.3 Example 5 Production Modifiedconjugated diene polymer F 4-(Aminomethyl)phenol *6 1.2 0.16 1.3 Example6 Production Modified conjugated diene polymer G 4-Hydroxybenzoic acid*7 1.4 0.18 1.3 Example 7 Production Modified conjugated diene polymer H4-Hydroxybenzyl alcohol *8 1.2 0.16 1.3 Example 8 Production Modifiedconjugated diene polymer I 4-[(2-Triethoxysilyl)ethylthio]phenol *9 2.60.34 1.3 Example 9 Production Unmodified conjugated diene polymer None 00 0 Example 10 <Remarks> The “Amount” indicates an amount (part(s) bymass) of the polar group-containing phenoxy compound added, relative to100 parts by mass of the unmodified conjugated diene polymer. The“Addition amount” indicates an amount (part(s) by mass) of the polargroup-containing phenoxy compound bonded to 100 parts by mass of themodified conjugated diene polymer. The “Modification degree” indicatesan amount [mmol (millimole)] of the polar group-containing phenoxycompound bonded in 100 g of the modified conjugated diene polymer. *1:L-Tyrosine, manufactured by Tokyo Chemical Industry Co., Ltd. *2:Peptide having tyrosine at the end (10AA), manufactured by Sigma-AldrichCo., LLC. *3: Protein having tyrosine at the end, manufactured bySigma-Aldrich Co., LLC. *4: Amidol, manufactured by Tokyo ChemicalIndustry Co., Ltd. *5: 4-Aminophenol, manufactured by Tokyo ChemicalIndustry Co., Ltd. *6: 4-(Aminomethyl)phenol, manufactured by TokyoChemical Industry Co., Ltd. *7: 4-Hydroxybenzoic acid, manufactured byTokyo Chemical Industry Co., Ltd. *8: 4-Hydroxybenzyl alcohol,manufactured by Tokyo Chemical Industry Co., Ltd. *9:4-[(2-Triethoxysilyl)ethylthio]phenol obtained in Production Example 9

Examples 1 to 9 and Comparative Example 1

According to the mixing formulations of the rubber compositions 1 and 2shown in Table 2, 20 types of rubber compositions in Examples 1 to 9 andComparative Example 1 were prepared by kneading by means of a Banburymixer which is an internal mixer. The prepared 20 types of rubbercompositions were individually vulcanized under conditions at 145° C.for 40 minutes, and then evaluated for the low-heat-generation property(tan δ index) and abrasion resistance (index). The results are shown inTable 3.

TABLE 2 Amount mixed (parts by mass) Formulation of rubber Rubber Rubbercomposition composition 1 composition 2 Rubber component *11 100 100Carbon black N339 *12 50 — Silica *13 — 55 Silane coupling agent *14 —5.5 Softening agent *15 5 10 Stearic acid 2 2 Antioxidant 6C *16 1 1Zinc oxide 3 3 Vulcanization accelerator 0.8 — DZ *17 Vulcanizationaccelerator — 1 DPG *18 Vulcanization accelerator — 1 DM *19Vulcanization accelerator — 1 NS *20 Sulfur 1 1.5 [Remarks] *11:Modified conjugated diene polymers A to K prepared in ProductionExamples 1 to 12 and unmodified conjugated diene polymer *12: N339,trade name “SEAST KH”, manufactured by Tokai Carbon Co., Ltd. *13: Wetprecipitated silica, trade name “Nipsil AQ”, manufactured by TosohSilica Corporation *14: Bis(3-triethoxysilylpropyl) disulfide (averagesulfur chain length: 2.35), silane coupling agent, trade name “Si75”(registered trademark), manufactured by Evonik *15: Process oil, tradename “A/O Mix”, manufactured by Sankyo Yuka Kogyo K.K. *16:N-(1,3-Dimethylbutyl)-N′-phenyl-p-phenylenediamine, trade name “Nocrac6C”, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. *17:N,N-Dicyclohexyl-2-benzothiazolyl sulfenamide, trade name “Nocceler DZ”,manufactured by Ouchi Shinko Chemical Industrial Co., Ltd. *18:1,3-Diphenylguanidine, trade name “Sanceler D”, manufactured by SanshinChemical Industry Co., Ltd. *19: Di-2-benzothiazolyl disulfide, tradename “Sanceler DM”, manufactured by Sanshin Chemical Industry Co., Ltd.*20: N-Tert-butyl-2-benzothiazolyl sulfenamide, trade name “SancelerNS”, manufactured by Sanshin Chemical Industry Co., Ltd.

TABLE 3 Comparative Example Example 1 2 3 4 5 6 7 8 9 1 Type of modifiedconjugated diene A B C D E F G H I Unmodified polymers A to I orunmodified conjugated, conjugated diene polymer diene polymer EvaluationLow-heat-generation 81 85 90 82 88 82 98 99 98 100 results for rubberproperty composition 1 (index) Abrasion resistance 119 115 110 118 112118 102 101 102 100 (index) Evaluation Low-heat-generation 53 63 67 5460 54 70 71 54 72 results for rubber property composition 2 (index)Abrasion resistance 123 111 106 122 114 122 103 101 122 100 (index)

As apparent from Table 3, with respect to each of the rubber composition1 which is a rubber composition having carbon black mixed thereinto andthe rubber composition 2 which is a rubber composition having silicamixed thereinto, the rubber compositions in Examples 1 to 9 hadexcellent low-heat-generation property (tan δ index) and excellentabrasion resistance (index), as compared to the rubber composition inComparative Example 1.

Production Example 11 (Modification Reaction Step for aStyrene-Butadiene Copolymer Rubber)

100 Parts by mass of a styrene-butadiene copolymer rubber (SBR, tradename “#1500”, manufactured by JSR Corporation) was chopped into 1 mmsquares, and added to 100 parts by mass of an acetate buffer (20 mM; pH:4.7), together with 1.8 parts by mass of tyrosine, and laccase (tradename “NS81268”, manufactured by Novozymes A/S; enzyme activity: 1,000(Unit/g); oxidation-reduction potential: 480 mV) was added in a 100(Unit/g×phr) addition unit amount relative to 100 parts by mass of thestyrene-butadiene copolymer rubber, and the resultant mixture wasstirred for one hour. Then, the mixture was dried using a hot-air dryerunder temperature conditions at 130° C. for 10 minutes to obtain amodified conjugated diene polymer J (modified styrene-butadienecopolymer rubber J). The “phr” has the same meaning as that of “part(s)by mass”.

Production Example 12 (Modification Reaction Step for aStyrene-Butadiene Copolymer Rubber)

A modified conjugated diene polymer K (styrene-butadiene copolymerrubber K) was obtained in the same manner as in Production Example 11except that no laccase was added.

The tyrosine addition amount and modification degree in ProductionExamples 11 and 12 are shown in Table 4.

TABLE 4 Type of Tyrosine polar group- Tyrosine addition Modifi-containing amount amount cation phenoxy (parts by (parts by degreeProduct compound mass) mass) (mmol) Production Modified Tyrosine *1, 1.80.12 0.65 Example 11 conjugated laccase diene added polymer J ProductionModified Tyrosine *1, 1.8 0 0 Example 12 conjugated no laccase dieneadded polymer K *1: L-Tyrosine, manufactured by Tokyo Chemical IndustryCo., Ltd.

Example 10 and Comparative Example 2

According to the mixing formulations of the rubber compositions 1 and 2shown in Table 2, two types of rubber compositions in Example 10 andComparative Example 2 were prepared by kneading by means of a Banburymixer which is an internal mixer. The prepared two types of rubbercompositions were individually vulcanized under conditions at 145° C.for 40 minutes, and then evaluated for the low-heat-generation property(tan δ index) and abrasion resistance (index). The results are shown inTable 5.

TABLE 5 Comparative Example Example 10 2 Modified Modified conjugatedconjugated diene diene Type of modified conjugated diene polymer polymerJ polymer K Evaluation results Low-heat-generation 90 106 for rubberproperty (index) composition 1 Abrasion resistance 110 105 (index)Evaluation results Low-heat-generation 60 74 for rubber property (index)composition 2 Abrasion resistance 120 106 (index)

As apparent from Table 5, with respect to each of the rubber composition1 which is a rubber composition having carbon black mixed thereinto andthe rubber composition 2 which is a rubber composition having silicamixed thereinto, the rubber composition in Example 10 had excellentlow-heat-generation property (tan δ index) and excellent abrasionresistance (index), as compared to the rubber composition in ComparativeExample 2.

INDUSTRIAL APPLICABILITY

By using the modified conjugated diene polymer of the present inventionas a rubber component of a rubber composition, a rubber compositionhaving excellent low-heat-generation property and excellent abrasionresistance can be obtained, and therefore is advantageously used as arubber composition for use in members for various types of tires(particularly, various pneumatic radial tires) for a passenger car, asmall-size truck, a light passenger car, a light truck, and a large-sizevehicle (for truck and bus, for off-road tire (for vehicle forconstruction, vehicle for mine, and the like)) and the like,particularly for use in members for tread of various pneumatic radialtires (especially a member for a tread grounding part).

1. A modified conjugated diene polymer in which a phenoxy group of apolar group-containing phenoxy compound is bonded to at least oneselected from the group consisting of the end, main chain, and sidechain of a conjugated diene polymer.
 2. The modified conjugated dienepolymer according to claim 1, wherein the polar group is at least oneselected from the group consisting of an amino group, an imino group, anitrile group, an ammonium group, an imide group, an amide group, ahydrazo group, an azo group, a diazo group, a sulfide group, a disulfidegroup, a sulfonyl group, a sulfinyl group, a thiocarbonyl group, ahydroxyl group, a carboxyl group, a carbonyl group, an epoxy group, anoxycarbonyl group, a nitrogen-containing heterocyclic group, anoxygen-containing heterocyclic group, a tin-containing group, and analkoxysilyl group.
 3. The modified conjugated diene polymer according toclaim 2, which has both an amino group and a carboxyl group as the polargroup.
 4. The modified conjugated diene polymer according to claim 1,wherein the polar group-containing phenoxy compound is at least oneselected from the group consisting of tyrosine, a peptide havingtyrosine, and a protein having tyrosine.
 5. The modified conjugateddiene polymer according to claim 1, wherein the amount of the polargroup-containing phenoxy compound bonded in 100 g of the modifiedconjugated diene polymer is from 0.005 to 55 mmol.
 6. The modifiedconjugated diene polymer according to claim 1, wherein the conjugateddiene polymer is natural rubber.
 7. A rubber composition comprising themodified conjugated diene polymer according to claim 1.